Oxidative stress, ubiquitination defects, and mitochondrial dysfunction are well recognized markers of various neurodegenerative diseases. This proposal is designed to elucidate the mechanism whereby the signaling scaffold, p62, regulates trafficking and removal of ubiquitinated proteins and damaged mitochondria. The specific aims of this proposal are based upon the CENTRAL HYPOTHESIS that p62 is involved in the transport of proteins to the proteasome or autophagosome, employing a common tag, K63-polyubiquitin. Sequestosome 1/p62 is predominantly expressed in the hippocampus, the center of learning and memory, where it serves as a scaffold to regulate the trafficking of K63-polyubiquitinated proteins and phosphorylation of atypical protein kinase C iota/lambda substrates. Gene-targeted deletion of p62 in mice causes oxidative stress leading to Alzheimer-like characteristics such as tau-phosphorylation, loss of short term memory and synaptic plasticity, reduced serum BDNF, depression, anxiety, along with accumulation of highly insoluble polyubiquitinated proteins in the adult mice. Humans with AD likewise exhibit reduced p62 levels in hippocampus that correlate with accumulation of insoluble polyubiquitinated tau. These findings suggest that a reduced amount of p62 may act in conjunction with other environmental or genetic factors to influence susceptibility to development of AD. Our long term goal is to understand the mechanism whereby removal of p62 in the brain results in oxidative stress that contributes to development of mouse AD. Our preliminary findings reveal that p62 converges upon HDAC6 to regulate it activity and thereby influences tubulin acetylation, leading to impaired clearance of aggregated proteins. Along with p62's role in autophagy the elimination of damaged mitochondria is impaired, which together with appearance of ubiquitin aggregates results in oxidative stress. The following specific aims are proposed to further elucidate the p62 regulatory pathway. Specific Aim 1 will examine the mechanism whereby p62 cooperates with HDAC6 to regulate clearance of aggregated polyubiquitinated proteins. Specific Aim 2 will examine the mechanism whereby p62 regulates the trafficking, clearance and energetics of mitochondria. Specific Aim 3 will define p62's role in mediating oxidative stress resistance. An innovative approach employing various complementary methods will be undertaken within the scope of the project. These findings are likely to provide insight into mechanism whereby p62 function impinges upon energetics and form of mitochondria, trafficking of interacting proteins, as well as, accumulation of polyubiquitin aggregates. Altogether, further knowledge of p62 may contribute to new treatments for AD, as well as, other neurodegenerative diseases. PUBLIC HEALTH RELEVANCE: This project will tease apart the function of the scaffolding protein p62. The innovative aspect of this project is that the role of p62 in trafficking of tau and other interacting proteins is largely undefined. P62 is a multifunctional protein involved in both of the two major protein degradation mechanisms, ubiquitin proteasome system and autophagy-lysosome pathway. The specific aims of this proposal are based upon the CENTRAL HYPOTHESIS that p62 is a novel shuttling factor that participates in the transport of proteins to the proteasome, autophagosome and removal of damaged mitochondria. Three synergistic but non-overlapping specific aims are proposed to further unravel the mechanistic details regarding the role of p62 in vivo. Aim 1 will illuminate the means by which p62 regulates clearance of aggregated proteins. Aim 2 will elucidate the mechanism whereby p62 regulates the trafficking and clearance of mitochondria. Aim 3 will define p62's role in mediating oxidative stress resistance. The results from this study will provide invaluable insights into the role of p62 in clearance of misfolded protein aggregates and neurodegeneration. These findings may provide an avenue to develop new therapeutics for the treatment of Alzheimer's disease as well as other neurodegenerative diseases, which possess disturbances in p62 expression as a component of their underlying pathophysiology.